<!DOCTYPE html>
<html lang="zh">
<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="ie=edge">
	<title></title>
	<style>
		.par{
			position: relative;
			width: 200px;
			height: 200px;
			left: 30px;
			background-color: #2196F3;
			z-index: 1;
		}
		.son{
			position: relative;
			left: -10px;
			width: 50%;
			height: 50%;
			background-color: red;
		}
		.grason{
			top: 60px;
			position: absolute;
			width: 50%;
			height: 50%;
			background-color: purple;
			z-index: -1;
		}
	</style>
</head>
<body>
	<div class="par">
		<div class="son">
			<div class="grason"></div>
		</div>
	</div>
</body>
</html>